In a conventional radio communication system for performing radio communication between a base station and a terminal, the base station can perform radio communication with facing the antenna toward the terminal by measuring a position of the terminal.
In such a position measurement, it is know that a base station transmits first and second signals from two or more antennas, and a mobile station determines a phase difference between the received first and second signals, calculates a direction of the mobile station viewed from the base station based on the phase difference, and transmits the data to the base station.
A radio station direction estimation apparatus, which estimates an arrival direction of a radio wave and estimates a position of the radio station by a ray trace method based on the estimated radio wave arrival direction and three-dimensional map data, is also known.
It is also known that a base station determines whether observed signal transmitted from a node is direct wave or reflected wave based on identification information of the observed signal and the interval of the observed signal, and corrects the distance between the node and the base station based on the determined result.    Patent Document 1: Japanese Laid-open Patent Publication No. 2001-237755    Patent Document 2: Japanese Laid-open Patent Publication No. 2006-170698    Patent Document 3: Japanese Laid-open Patent Publication No. 2007-155523
However in a multi-path environment where direct wave and reflected wave coexist, the base station, in some cases, may receive both direct wave and reflected wave. In the above mentioned prior art, which determines a phase difference between two signals, or which estimates the arrival direction of radio wave, the multi-path environment is not considered, therefore the position of the terminal cannot be measured at high precision.
In the case of the above mentioned prior art, which determines whether the receive wave is the direct wave or reflected wave, the distance of the base station and the node is determined based on the result of determining whether the received wave is the direct wave or reflected wave, and determining the position of the node is not considered. Therefore in this prior art as well, the position of the terminal cannot be measured at high precision.